The present invention relates in general to a network management system. More particularly, the invention relates to a network management system for managing a network system to which a plurality of networks the address systems of which are different from one another are connected.
IP addresses as network addresses which are currently most widely utilized in the Internet and the like are prescribed in accordance with the protocol called the IPv4 (Internet Protocol ver. 4) and also are addresses each having the address space of 32 bits. The network addresses must be uniquely allocated to apparatuses connected to the network, respectively, and hence the allocation of the network addresses to the apparatuses connected to the Internet has been carried out by the organ called NIC or the like in such a way as to become unique. Since in the IPv4, each of the IP addresses has the address space of 32 bits, the addresses of 2 to the 32-th power, i.e., four billions at maximum can be theoretically allocated. However, as the number of apparatuses connected to the Internet is increased, it becomes difficult to allocate the IP addresses of the IPv4 to all of the apparatuses connected to the Internet.
The technique which is widely used as the technique for solving the above-mentioned problem is the method wherein the address translation function described in RFC1631 (The IP Network Address Translator) decided by the IETF is combined with the private network described in RFC1918 (Address Allocation for Private Internets). The method is established on the assumption that for example, all of the apparatuses which are present in the local network such as the network within industry are not necessarily connected to the external network such as the Internet. In other words, first of all, the local network such as network within industry allocates the IP address using the address which falls within the private address described in RFC1918 to construct the network. At this time, with this private address, the associated apparatuses are not connected to the external network such as the Internet. With respect to the apparatuses connected to the external network such as the Internet, the address translator described in RFC1613 is disposed between the local network and the external network such as the Internet, and the address of the transmission/reception packet is translated through the address translation from the private address into the global address with which the access is given to the Internet, thereby making the connection to the Internet possible. Now, by the global address is meant the address which is allocated by the NIC or the like. At this time, there is also made the device in which the infinite global addresses are effectively utilized in such a way that the global addresses are dynamically allocated to make it possible that a plurality of local nodes hold one global address in common on the basis of the time-sharing.
Now, in the address translation described in RFC1631, the rewriting of the transmission source IP address and the transmission destination IP address which are contained in the header of the IP packet, and the change of the check sum of the IP header which is generated along with the rewriting are recalculated to replace them with each other. As a result, the communication by TCP/IP becomes possible, and the communication according to the protocol of the upper layer with respect thereto also becomes possible.
However, though in the network management protocol such as the SNMP, the IP address is contained in a protocol data unit (PDU) as well in which the data is exchanged in accordance with the management protocol, this part is not subjected to the address translation in the address translator described in RFC1631.
On the other hand, in JP-A-11-187058, in addition to the function of the address translation described in RFC1631, the address translator having the function of carrying out the address translation with respect to the protocol data unit as well of the management protocol is described.